PCI: Add pcie_flags_reg to cache PCIe capabilities register

Since PCI Express Capabilities Register is read only, cache its value
into struct pci_dev to avoid repeatedly calling pci_read_config_*().
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/probe.c

@@ -929,7 +929,8 @@ void set_pcie_port_type(struct pci_dev *pdev)
 	pdev->is_pcie = 1;
 	pdev->pcie_cap = pos;
 	pci_read_config_word(pdev, pos + PCI_EXP_FLAGS, &reg16);
-	pdev->pcie_type = (reg16 & PCI_EXP_FLAGS_TYPE) >> 4;
+	pdev->pcie_flags_reg = reg16;
+	pdev->pcie_type = pci_pcie_type(pdev);
 	pci_read_config_word(pdev, pos + PCI_EXP_DEVCAP, &reg16);
 	pdev->pcie_mpss = reg16 & PCI_EXP_DEVCAP_PAYLOAD;
 }

include/linux/pci.h

@@ -258,6 +258,7 @@ struct pci_dev {
 	u8		pcie_mpss:3;	/* PCI-E Max Payload Size Supported */
 	u8		rom_base_reg;	/* which config register controls the ROM */
 	u8		pin;  		/* which interrupt pin this device uses */
+	u16		pcie_flags_reg;	/* cached PCI-E Capabilities Register */
 
 	struct pci_driver *driver;	/* which driver has allocated this device */
 	u64		dma_mask;	/* Mask of the bits of bus address this
@@ -1650,6 +1651,15 @@ static inline bool pci_is_pcie(struct pci_dev *dev)
 	return !!pci_pcie_cap(dev);
 }
 
+/**
+ * pci_pcie_type - get the PCIe device/port type
+ * @dev: PCI device
+ */
+static inline int pci_pcie_type(const struct pci_dev *dev)
+{
+	return (dev->pcie_flags_reg & PCI_EXP_FLAGS_TYPE) >> 4;
+}
+
 void pci_request_acs(void);
 bool pci_acs_enabled(struct pci_dev *pdev, u16 acs_flags);
 bool pci_acs_path_enabled(struct pci_dev *start,